Methods and systems disclosed herein relate generally to unmanned underwater vehicles (UUVs) and more specifically to navigation for UUVs.
UUVs are expected to perform missions previously assigned to manned vessels. Autonomous navigation for these vehicles is a technical challenge, certainly a critical performance factor. The race to find accurate and robust navigation methods is a key part of UUV development. Use of UUVs to replace manned platforms can potentially save billions of dollars, remove sailors from risky environments, and reduce greenhouse gas emissions. Currently, navigation is performed by communication between the UUV and a host ship.
Terrain following navigation, which has worked well for unmanned aerial vehicles, has been proposed for UUVs. However, much of the ocean is devoid of terrain features. Terrain following vehicles transiting long distances would require powerful sonars which sense a wide footprint of the ocean floor. Certain bottom-following controllers designed for UUVs take into account the bathymetric characteristics ahead of the UUV as measured by echo sounders. Navigation off two-dimensional surface elevation terrain data sets has been performed, but in demonstrations, the elevation varied by more than 800 m in a 3.6 km distance, corresponding to at least a 13° slope (the average slope on the continental shelf is about 0.1°).
A normal incidence (unsteered) beam has been used that collects a depth profile of acoustic reflectivity along a track over which the UUV progresses. Being two-dimensional, this method cannot be used for navigation.
What are needed are systems and methods for navigating UUVs and ultimately for replacing manned platforms with UUVs. What are further needed are systems and methods for acoustically sensing and exploiting sub-bottom features (e.g. sand/mud layers, linear features like pipelines, or point scatterers, such as shells) for navigation of UUVs. What is still further needed is a system that includes a three dimensional data set provided by a sub-bottom profiler (SBP) and achieved through beam steering. Bottom-penetrating sonar could sense features in the sub-bottom to use for navigation. Depending on the morphology of a specific area, it is expected that the sub-bottom would be richer in features than much of the seafloor. Given that little of the seafloor sub-bottom structure has been mapped, navigation from sub-bottom features may require a pre-mission survey. This task can also be performed by a UUV in a less time-constrained period than an actual operational cruise. Known features, such as, for example, but not limited to, buried pipelines or cables, could be exploited. In this situation, a prior survey may not be required. The point of navigating off sub-bottom features to diminish the reliance on the rare areas of the ocean where there are terrain features distinct and dramatic enough to reliably navigate off of.